.\"
.\" Copyright (c) 2009-2018 Todd C. Miller <Todd.Miller@sudo.ws>
.\"
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.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
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.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
.\" ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
.Dd June 1, 2018
.Dt SUDO_PLUGIN @mansectform@
.Os Sudo @PACKAGE_VERSION@
.Sh NAME
.Nm sudo_plugin
.Nd Sudo Plugin API
.Sh DESCRIPTION
Starting with version 1.8,
.Nm sudo
supports a plugin API
for policy and session logging.
Plugins may be compiled as dynamic shared objects (the default on
systems that support them) or compiled statically into the
.Nm sudo
binary itself.
By default, the
.Nm sudoers
policy plugin and an associated I/O logging plugin are used.
Via the plugin API,
.Nm sudo
can be configured to use alternate policy and/or I/O logging plugins
provided by third parties.
The plugins to be used are specified in the
.Xr sudo.conf @mansectform@
file.
.Pp
The API is versioned with a major and minor number.
The minor version number is incremented when additions are made.
The major number is incremented when incompatible changes are made.
A plugin should be check the version passed to it and make sure that the
major version matches.
.Pp
The plugin API is defined by the
.Li sudo_plugin.h
header file.
.Ss Policy plugin API
A policy plugin must declare and populate a
.Li policy_plugin
struct in the global scope.
This structure contains pointers to the functions that implement the
.Nm sudo
policy checks.
The name of the symbol should be specified in
.Xr sudo.conf @mansectform@
along with a path to the plugin so that
.Nm sudo
can load it.
.Bd -literal
struct policy_plugin {
#define SUDO_POLICY_PLUGIN     1
    unsigned int type; /* always SUDO_POLICY_PLUGIN */
    unsigned int version; /* always SUDO_API_VERSION */
    int (*open)(unsigned int version, sudo_conv_t conversation,
                sudo_printf_t plugin_printf, char * const settings[],
                char * const user_info[], char * const user_env[],
                char * const plugin_options[]);
    void (*close)(int exit_status, int error);
    int (*show_version)(int verbose);
    int (*check_policy)(int argc, char * const argv[],
                        char *env_add[], char **command_info[],
                        char **argv_out[], char **user_env_out[]);
    int (*list)(int argc, char * const argv[], int verbose,
                const char *list_user);
    int (*validate)(void);
    void (*invalidate)(int remove);
    int (*init_session)(struct passwd *pwd, char **user_env[]);
    void (*register_hooks)(int version,
       int (*register_hook)(struct sudo_hook *hook));
    void (*deregister_hooks)(int version,
       int (*deregister_hook)(struct sudo_hook *hook));
};
.Ed
.Pp
The policy_plugin struct has the following fields:
.Bl -tag -width 4n
.It type
The
.Li type
field should always be set to SUDO_POLICY_PLUGIN.
.It version
The
.Li version
field should be set to
.Dv SUDO_API_VERSION .
.Pp
This allows
.Nm sudo
to determine the API version the plugin was
built against.
.It open
.Bd -literal -compact
int (*open)(unsigned int version, sudo_conv_t conversation,
            sudo_printf_t plugin_printf, char * const settings[],
            char * const user_info[], char * const user_env[],
            char * const plugin_options[]);
.Ed
.Pp
Returns 1 on success, 0 on failure, \-1 if a general error occurred,
or \-2 if there was a usage error.
In the latter case,
.Nm sudo
will print a usage message before it exits.
If an error occurs, the plugin may optionally call the
.Fn conversation
or
.Fn plugin_printf
function with
.Dv SUDO_CONF_ERROR_MSG
to present additional error information to the user.
.Pp
The function arguments are as follows:
.Bl -tag -width 4n
.It version
The version passed in by
.Nm sudo
allows the plugin to determine the
major and minor version number of the plugin API supported by
.Nm sudo .
.It conversation
A pointer to the
.Fn conversation
function that can be used by the plugin to interact with the user (see below).
Returns 0 on success and \-1 on failure.
.It plugin_printf
A pointer to a
.Fn printf Ns -style
function that may be used to display informational or error messages
(see below).
Returns the number of characters printed on success and \-1 on failure.
.It settings
A vector of user-supplied
.Nm sudo
settings in the form of
.Dq name=value
strings.
The vector is terminated by a
.Dv NULL
pointer.
These settings correspond to flags the user specified when running
.Nm sudo .
As such, they will only be present when the corresponding flag has
been specified on the command line.
.Pp
When parsing
.Em settings ,
the plugin should split on the
.Sy first
equal sign
.Pq Ql =
since the
.Em name
field will never include one
itself but the
.Em value
might.
.Bl -tag -width 4n
.It bsdauth_type=string
Authentication type, if specified by the
.Fl a
flag, to use on
systems where BSD authentication is supported.
.It closefrom=number
If specified, the user has requested via the
.Fl C
flag that
.Nm sudo
close all files descriptors with a value of
.Em number
or higher.
The plugin may optionally pass this, or another value, back in the
.Em command_info
list.
.It debug_flags=string
A debug file path name followed by a space and a comma-separated
list of debug flags that correspond to the plugin's
.Li Debug
entry in
.Xr sudo.conf @mansectform@ ,
if there is one.
The flags are passed to the plugin exactly as they appear in
.Xr sudo.conf @mansectform@ .
The syntax used by
.Nm sudo
and the
.Nm sudoers
plugin is
.Em subsystem Ns @ Ns Em priority
but a plugin is free to use a different
format so long as it does not include a comma
.Pq Ql ,\& .
Prior to
.Nm sudo
1.8.12, there was no way to specify plugin-specific
.Em debug_flags
so the value was always the same as that used by the
.Nm sudo
front end and did not include a path name, only the flags themselves.
As of version 1.7 of the plugin interface,
.Nm sudo
will only pass
.Em debug_flags
if
.Xr sudo.conf @mansectform@
contains a plugin-specific
.Li Debug
entry.
.It debug_level=number
This setting has been deprecated in favor of
.Em debug_flags .
.It ignore_ticket=bool
Set to true if the user specified the
.Fl k
flag along with a
command, indicating that the user wishes to ignore any cached
authentication credentials.
.Em implied_shell
to true.
This allows
.Nm sudo
with no arguments
to be used similarly to
.Xr su 1 .
If the plugin does not to support this usage, it may return a value of \-2
from the
.Fn check_policy
function, which will cause
.Nm sudo
to print a usage message and
exit.
.It implied_shell=bool
If the user does not specify a program on the command line,
.Nm sudo
will pass the plugin the path to the user's shell and set
.It login_class=string
BSD login class to use when setting resource limits and nice value,
if specified by the
.Fl c
flag.
.It login_shell=bool
Set to true if the user specified the
.Fl i
flag, indicating that
the user wishes to run a login shell.
.It max_groups=int
The maximum number of groups a user may belong to.
This will only be present if there is a corresponding setting in
.Xr sudo.conf @mansectform@ .
.It network_addrs=list
A space-separated list of IP network addresses and netmasks in the
form
.Dq addr/netmask ,
e.g.\&
.Dq 192.168.1.2/255.255.255.0 .
The address and netmask pairs may be either IPv4 or IPv6, depending on
what the operating system supports.
If the address contains a colon
.Pq Ql :\& ,
it is an IPv6 address, else it is IPv4.
.It noninteractive=bool
Set to true if the user specified the
.Fl n
flag, indicating that
.Nm sudo
should operate in non-interactive mode.
The plugin may reject a command run in non-interactive mode if user
interaction is required.
.It plugin_dir=string
The default plugin directory used by the
.Nm sudo
front end.
This is the default directory set at compile time and may not
correspond to the directory the running plugin was loaded from.
It may be used by a plugin to locate support files.
.It plugin_path=string
The path name of plugin loaded by the
.Nm sudo
front end.
The path name will be a fully-qualified unless the plugin was
statically compiled into
.Nm sudo .
.It preserve_environment=bool
Set to true if the user specified the
.Fl E
flag, indicating that
the user wishes to preserve the environment.
.It preserve_groups=bool
Set to true if the user specified the
.Fl P
flag, indicating that
the user wishes to preserve the group vector instead of setting it
based on the runas user.
.It progname=string
The command name that sudo was run as, typically
.Dq sudo
or
.Dq sudoedit .
.It prompt=string
The prompt to use when requesting a password, if specified via
the
.Fl p
flag.
.It remote_host=string
The name of the remote host to run the command on, if specified via
the
.Fl h
option.
Support for running the command on a remote host is meant to be implemented
via a helper program that is executed in place of the user-specified command.
The
.Nm sudo
front end is only capable of executing commands on the local host.
Only available starting with API version 1.4.
.It run_shell=bool
Set to true if the user specified the
.Fl s
flag, indicating that the user wishes to run a shell.
.It runas_group=string
The group name or gid to run the command as, if specified via
the
.Fl g
flag.
.It runas_user=string
The user name or uid to run the command as, if specified via the
.Fl u
flag.
.It selinux_role=string
SELinux role to use when executing the command, if specified by
the
.Fl r
flag.
.It selinux_type=string
SELinux type to use when executing the command, if specified by
the
.Fl t
flag.
.It set_home=bool
Set to true if the user specified the
.Fl H
flag.
If true, set the
.Li HOME
environment variable to the target user's home directory.
.It sudoedit=bool
Set to true when the
.Fl e
flag is is specified or if invoked as
.Nm sudoedit .
The plugin shall substitute an editor into
.Em argv
in the
.Fn check_policy
function or return \-2 with a usage error
if the plugin does not support
.Em sudoedit .
For more information, see the
.Em check_policy
section.
.It timeout=string
User-specified command timeout.
Not all plugins support command timeouts and the ability for the
user to set a timeout may be restricted by policy.
The format of the timeout string is plugin-specific.
.El
.Pp
Additional settings may be added in the future so the plugin should
silently ignore settings that it does not recognize.
.It user_info
A vector of information about the user running the command in the form of
.Dq name=value
strings.
The vector is terminated by a
.Dv NULL
pointer.
.Pp
When parsing
.Em user_info ,
the plugin should split on the
.Sy first
equal sign
.Pq Ql =
since the
.Em name
field will never include one
itself but the
.Em value
might.
.Bl -tag -width 4n
.It cols=int
The number of columns the user's terminal supports.
If there is no terminal device available, a default value of 80 is used.
.It cwd=string
The user's current working directory.
.It egid=gid_t
The effective group ID of the user invoking
.Nm sudo .
.It euid=uid_t
The effective user ID of the user invoking
.Nm sudo .
.It gid=gid_t
The real group ID of the user invoking
.Nm sudo .
.It groups=list
The user's supplementary group list formatted as a string of
comma-separated group IDs.
.It host=string
The local machine's hostname as returned by the
.Xr gethostname 2
system call.
.It lines=int
The number of lines the user's terminal supports.
If there is
no terminal device available, a default value of 24 is used.
.It pgid=int
The ID of the process group that the running
.Nm sudo
process is a member of.
Only available starting with API version 1.2.
.It pid=int
The process ID of the running
.Nm sudo
process.
Only available starting with API version 1.2.
.It plugin_options
Any (non-comment) strings immediately after the plugin path are
passed as arguments to the plugin.
These arguments are split on a white space boundary and are passed to
the plugin in the form of a
.Dv NULL Ns -terminated
array of strings.
If no arguments were
specified,
.Em plugin_options
will be the
.Dv NULL
pointer.
.Pp
NOTE: the
.Em plugin_options
parameter is only available starting with
API version 1.2.
A plugin
.Sy must
check the API version specified
by the
.Nm sudo
front end before using
.Em plugin_options .
Failure to do so may result in a crash.
.It ppid=int
The parent process ID of the running
.Nm sudo
process.
Only available starting with API version 1.2.
.It sid=int
The session ID of the running
.Nm sudo
process or 0 if
.Nm sudo
is not part of a POSIX job control session.
Only available starting with API version 1.2.
.It tcpgid=int
The ID of the foreground process group associated with the terminal
device associated with the
.Nm sudo
process or \-1 if there is no
terminal present.
Only available starting with API version 1.2.
.It tty=string
The path to the user's terminal device.
If the user has no terminal device associated with the session,
the value will be empty, as in
.Dq Li tty= .
.It uid=uid_t
The real user ID of the user invoking
.Nm sudo .
.It umask=octal
The invoking user's file creation mask.
Only available starting with API version 1.10.
.It user=string
The name of the user invoking
.Nm sudo .
.El
.It user_env
The user's environment in the form of a
.Dv NULL Ns -terminated vector of
.Dq name=value
strings.
.Pp
When parsing
.Em user_env ,
the plugin should split on the
.Sy first
equal sign
.Pq Ql =
since the
.Em name
field will never include one
itself but the
.Em value
might.
.El
.It close
.Bd -literal -compact
void (*close)(int exit_status, int error);
.Ed
.Pp
The
.Fn close
function is called when the command being run by
.Nm sudo
finishes.
.Pp
The function arguments are as follows:
.Bl -tag -width 4n
.It exit_status
The command's exit status, as returned by the
.Xr wait 2
system call.
The value of
.Li exit_status
is undefined if
.Li error
is non-zero.
.It error
If the command could not be executed, this is set to the value of
.Li errno
set by the
.Xr execve 2
system call.
The plugin is responsible for displaying error information via the
.Fn conversation
or
.Fn plugin_printf
function.
If the command was successfully executed, the value of
.Li error
is 0.
.El
.Pp
If no
.Fn close
function is defined, no I/O logging plugins are loaded,
and neither the
.Em timeout
not
.Em use_pty
options are set in the
.Li command_info
list, the
.Nm sudo
front end may execute the command directly instead of running
it as a child process.
.It show_version
.Bd -literal -compact
int (*show_version)(int verbose);
.Ed
.Pp
The
.Fn show_version
function is called by
.Nm sudo
when the user specifies
the
.Fl V
option.
The plugin may display its version information to the user via the
.Fn conversation
or
.Fn plugin_printf
function using
.Dv SUDO_CONV_INFO_MSG .
If the user requests detailed version information, the verbose flag will be set.
.It check_policy
.Bd -literal -compact
int (*check_policy)(int argc, char * const argv[]
                    char *env_add[], char **command_info[],
                    char **argv_out[], char **user_env_out[]);
.Ed
.Pp
The
.Fn check_policy
function is called by
.Nm sudo
to determine
whether the user is allowed to run the specified commands.
.Pp
If the
.Em sudoedit
option was enabled in the
.Em settings
array
passed to the
.Fn open
function, the user has requested
.Em sudoedit
mode.
.Em sudoedit
is a mechanism for editing one or more files
where an editor is run with the user's credentials instead of with
elevated privileges.
.Nm sudo
achieves this by creating user-writable
temporary copies of the files to be edited and then overwriting the
originals with the temporary copies after editing is complete.
If the plugin supports
.Em sudoedit ,
it should choose the editor to be used, potentially from a variable
in the user's environment, such as
.Li EDITOR ,
and include it in
.Em argv_out
(note that environment
variables may include command line flags).
The files to be edited should be copied from
.Em argv
into
.Em argv_out ,
separated from the
editor and its arguments by a
.Dq Li --
element.
The
.Dq Li --
will
be removed by
.Nm sudo
before the editor is executed.
The plugin should also set
.Em sudoedit=true
in the
.Em command_info
list.
.Pp
The
.Fn check_policy
function returns 1 if the command is allowed,
0 if not allowed, \-1 for a general error, or \-2 for a usage error
or if
.Em sudoedit
was specified but is unsupported by the plugin.
In the latter case,
.Nm sudo
will print a usage message before it
exits.
If an error occurs, the plugin may optionally call the
.Fn conversation
or
.Fn plugin_printf
function with
.Dv SUDO_CONF_ERROR_MSG
to present additional error information to the user.
.Pp
The function arguments are as follows:
.Bl -tag -width 4n
.It argc
The number of elements in
.Em argv ,
not counting the final
.Dv NULL
pointer.
.It argv
The argument vector describing the command the user wishes to run,
in the same form as what would be passed to the
.Xr execve 2
system call.
The vector is terminated by a
.Dv NULL
pointer.
.It env_add
Additional environment variables specified by the user on the command
line in the form of a
.Dv NULL Ns -terminated
vector of
.Dq name=value
strings.
The plugin may reject the command if one or more variables
are not allowed to be set, or it may silently ignore such variables.
.Pp
When parsing
.Em env_add ,
the plugin should split on the
.Sy first
equal sign
.Pq Ql =
since the
.Em name
field will never include one
itself but the
.Em value
might.
.It command_info
Information about the command being run in the form of
.Dq name=value
strings.
These values are used by
.Nm sudo
to set the execution
environment when running a command.
The plugin is responsible for creating and populating the vector,
which must be terminated with a
.Dv NULL
pointer.
The following values are recognized by
.Nm sudo :
.Bl -tag -width 4n
.It chroot=string
The root directory to use when running the command.
.It closefrom=number
If specified,
.Nm sudo
will close all files descriptors with a value
of
.Em number
or higher.
.It command=string
Fully qualified path to the command to be executed.
.It cwd=string
The current working directory to change to when executing the command.
.It exec_background=bool
By default,
.Nm sudo
runs a command as the foreground process as long as
.Nm sudo
itself is running in the foreground.
When
.Em exec_background
is enabled and the command is being run in a pty (due to I/O logging
or the
.Em use_pty
setting), the command will be run as a background process.
Attempts to read from the controlling terminal (or to change terminal
settings) will result in the command being suspended with the
.Dv SIGTTIN
signal (or
.Dv SIGTTOU
in the case of terminal settings).
If this happens when
.Nm sudo
is a foreground process, the command will be granted the controlling terminal
and resumed in the foreground with no user intervention required.
The advantage of initially running the command in the background is that
.Nm sudo
need not read from the terminal unless the command explicitly requests it.
Otherwise, any terminal input must be passed to the command, whether it
has required it or not (the kernel buffers terminals so it is not possible
to tell whether the command really wants the input).
This is different from historic
.Em sudo
behavior or when the command is not being run in a pty.
.Pp
For this to work seamlessly, the operating system must support the
automatic restarting of system calls.
Unfortunately, not all operating systems do this by default,
and even those that do may have bugs.
For example, macOS fails to restart the
.Fn tcgetattr
and
.Fn tcsetattr
system calls (this is a bug in macOS).
Furthermore, because this behavior depends on the command stopping with the
.Dv SIGTTIN
or
.Dv SIGTTOU
signals, programs that catch these signals and suspend themselves
with a different signal (usually
.Dv SIGTOP )
will not be automatically foregrounded.
Some versions of the linux
.Xr su 1
command behave this way.
Because of this, a plugin should not set
.Em exec_background
unless it is explicitly enabled by the administrator and there should
be a way to enabled or disable it on a per-command basis.
.Pp
This setting has no effect unless I/O logging is enabled or
.Em use_pty
is enabled.
.It execfd=number
If specified,
.Nm sudo
will use the
.Xr fexecve 2
system call to execute the command instead of
.Xr execve 2 .
The specified
.Em number
must refer to an open file descriptor.
.It iolog_compress=bool
Set to true if the I/O logging plugins, if any, should compress the
log data.
This is a hint to the I/O logging plugin which may choose to ignore it.
.It iolog_group=string
The group that will own newly created I/O log files and directories.
This is a hint to the I/O logging plugin which may choose to ignore it.
.It iolog_mode=octal
The file permission mode to use when creating I/O log files and directories.
This is a hint to the I/O logging plugin which may choose to ignore it.
.It iolog_user=string
The user that will own newly created I/O log files and directories.
This is a hint to the I/O logging plugin which may choose to ignore it.
.It iolog_path=string
Fully qualified path to the file or directory in which I/O log is
to be stored.
This is a hint to the I/O logging plugin which may choose to ignore it.
If no I/O logging plugin is loaded, this setting has no effect.
.It iolog_stdin=bool
Set to true if the I/O logging plugins, if any, should log the
standard input if it is not connected to a terminal device.
This is a hint to the I/O logging plugin which may choose to ignore it.
.It iolog_stdout=bool
Set to true if the I/O logging plugins, if any, should log the
standard output if it is not connected to a terminal device.
This is a hint to the I/O logging plugin which may choose to ignore it.
.It iolog_stderr=bool
Set to true if the I/O logging plugins, if any, should log the
standard error if it is not connected to a terminal device.
This is a hint to the I/O logging plugin which may choose to ignore it.
.It iolog_ttyin=bool
Set to true if the I/O logging plugins, if any, should log all
terminal input.
This only includes input typed by the user and not from a pipe or
redirected from a file.
This is a hint to the I/O logging plugin which may choose to ignore it.
.It iolog_ttyout=bool
Set to true if the I/O logging plugins, if any, should log all
terminal output.
This only includes output to the screen, not output to a pipe or file.
This is a hint to the I/O logging plugin which may choose to ignore it.
.It login_class=string
BSD login class to use when setting resource limits and nice value
(optional).
This option is only set on systems that support login classes.
.It nice=int
Nice value (priority) to use when executing the command.
The nice value, if specified, overrides the priority associated with the
.Em login_class
on BSD systems.
.It noexec=bool
If set, prevent the command from executing other programs.
.It preserve_fds=list
A comma-separated list of file descriptors that should be
preserved, regardless of the value of the
.Em closefrom
setting.
Only available starting with API version 1.5.
.It preserve_groups=bool
If set,
.Nm sudo
will preserve the user's group vector instead of
initializing the group vector based on
.Li runas_user .
.It runas_egid=gid
Effective group ID to run the command as.
If not specified, the value of
.Em runas_gid
is used.
.It runas_euid=uid
Effective user ID to run the command as.
If not specified, the value of
.Em runas_uid
is used.
.It runas_gid=gid
Group ID to run the command as.
.It runas_groups=list
The supplementary group vector to use for the command in the form
of a comma-separated list of group IDs.
If
.Em preserve_groups
is set, this option is ignored.
.It runas_uid=uid
User ID to run the command as.
.It selinux_role=string
SELinux role to use when executing the command.
.It selinux_type=string
SELinux type to use when executing the command.
.It set_utmp=bool
Create a utmp (or utmpx) entry when a pseudo-tty is allocated.
By default, the new entry will be a copy of the user's existing utmp
entry (if any), with the tty, time, type and pid fields updated.
.It sudoedit=bool
Set to true when in
.Em sudoedit
mode.
The plugin may enable
.Em sudoedit
mode even if
.Nm sudo
was not invoked as
.Nm sudoedit .
This allows the plugin to perform command substitution and transparently
enable
.Em sudoedit
when the user attempts to run an editor.
.It sudoedit_checkdir=bool
Set to false to disable directory writability checks in
.Nm sudoedit .
By default,
.Nm sudoedit
1.8.16 and higher will check all directory components of the path to be
edited for writability by the invoking user.
Symbolic links will not be followed in writable directories and
.Nm sudoedit
will refuse to edit a file located in a writable directory.
These restrictions are not enforced when
.Nm sudoedit
is run by root.
The
.Em sudoedit_follow
option can be set to false to disable this check.
Only available starting with API version 1.8.
.It sudoedit_follow=bool
Set to true to allow
.Nm sudoedit
to edit files that are symbolic links.
By default,
.Nm sudoedit
1.8.15 and higher will refuse to open a symbolic link.
The
.Em sudoedit_follow
option can be used to restore the older behavior and allow
.Nm sudoedit
to open symbolic links.
Only available starting with API version 1.8.
.It timeout=int
Command timeout.
If non-zero then when the timeout expires the command will be killed.
.It umask=octal
The file creation mask to use when executing the command.
.It use_pty=bool
Allocate a pseudo-tty to run the command in, regardless of whether
or not I/O logging is in use.
By default,
.Nm sudo
will only run
the command in a pty when an I/O log plugin is loaded.
.It utmp_user=string
User name to use when constructing a new utmp (or utmpx) entry when
.Em set_utmp
is enabled.
This option can be used to set the user field in the utmp entry to
the user the command runs as rather than the invoking user.
If not set,
.Nm sudo
will base the new entry on
the invoking user's existing entry.
.El
.Pp
Unsupported values will be ignored.
.It argv_out
The
.Dv NULL Ns -terminated
argument vector to pass to the
.Xr execve 2
system call when executing the command.
The plugin is responsible for allocating and populating the vector.
.It user_env_out
The
.Dv NULL Ns -terminated
environment vector to use when executing the command.
The plugin is responsible for allocating and populating the vector.
.El
.It list
.Bd -literal -compact
int (*list)(int verbose, const char *list_user,
            int argc, char * const argv[]);
.Ed
.Pp
List available privileges for the invoking user.
Returns 1 on success, 0 on failure and \-1 on error.
On error, the plugin may optionally call the
.Fn conversation
or
.Fn plugin_printf
function with
.Dv SUDO_CONF_ERROR_MSG
to present additional error information to
the user.
.Pp
Privileges should be output via the
.Fn conversation
or
.Fn plugin_printf
function using
.Dv SUDO_CONV_INFO_MSG ,
.Bl -tag -width 4n
.It verbose
Flag indicating whether to list in verbose mode or not.
.It list_user
The name of a different user to list privileges for if the policy
allows it.
If
.Dv NULL ,
the plugin should list the privileges of the invoking user.
.It argc
The number of elements in
.Em argv ,
not counting the final
.Dv NULL
pointer.
.It argv
If
.No non- Ns Dv NULL ,
an argument vector describing a command the user
wishes to check against the policy in the same form as what would
be passed to the
.Xr execve 2
system call.
If the command is permitted by the policy, the fully-qualified path
to the command should be displayed along with any command line arguments.
.El
.It validate
.Bd -literal -compact
int (*validate)(void);
.Ed
.Pp
The
.Fn validate
function is called when
.Nm sudo
is run with the
.Fl v
flag.
For policy plugins such as
.Nm sudoers
that cache
authentication credentials, this function will validate and cache
the credentials.
.Pp
The
.Fn validate
function should be
.Dv NULL
if the plugin does not support credential caching.
.Pp
Returns 1 on success, 0 on failure and \-1 on error.
On error, the plugin may optionally call the
.Fn conversation
or
.Fn plugin_printf
function with
.Dv SUDO_CONF_ERROR_MSG
to present additional
error information to the user.
.It invalidate
.Bd -literal -compact
void (*invalidate)(int remove);
.Ed
.Pp
The
.Fn invalidate
function is called when
.Nm sudo
is called with
the
.Fl k
or
.Fl K
flag.
For policy plugins such as
.Nm sudoers
that
cache authentication credentials, this function will invalidate the
credentials.
If the
.Em remove
flag is set, the plugin may remove
the credentials instead of simply invalidating them.
.Pp
The
.Fn invalidate
function should be
.Dv NULL
if the plugin does not support credential caching.
.It init_session
.Bd -literal -compact
int (*init_session)(struct passwd *pwd, char **user_envp[);
.Ed
.Pp
The
.Fn init_session
function is called before
.Nm sudo
sets up the
execution environment for the command.
It is run in the parent
.Nm sudo
process and before any uid or gid changes.
This can be used to perform session setup that is not supported by
.Em command_info ,
such as opening the PAM session.
The
.Fn close
function can be
used to tear down the session that was opened by
.Li init_session .
.Pp
The
.Em pwd
argument points to a passwd struct for the user the
command will be run as if the uid the command will run as was found
in the password database, otherwise it will be
.Dv NULL .
.Pp
The
.Em user_env
argument points to the environment the command will
run in, in the form of a
.Dv NULL Ns -terminated
vector of
.Dq name=value
strings.
This is the same string passed back to the front end via
the Policy Plugin's
.Em user_env_out
parameter.
If the
.Fn init_session
function needs to modify the user environment, it should update the
pointer stored in
.Em user_env .
The expected use case is to merge the contents of the PAM environment
(if any) with the contents of
.Em user_env .
NOTE: the
.Em user_env
parameter is only available
starting with API version 1.2.
A plugin
.Sy must
check the API
version specified by the
.Nm sudo
front end before using
.Em user_env .
Failure to do so may result in a crash.
.Pp
Returns 1 on success, 0 on failure and \-1 on error.
On error, the plugin may optionally call the
.Fn conversation
or
.Fn plugin_printf
function with
.Dv SUDO_CONF_ERROR_MSG
to present additional
error information to the user.
.It register_hooks
.Bd -literal -compact
void (*register_hooks)(int version,
   int (*register_hook)(struct sudo_hook *hook));
.Ed
.Pp
The
.Fn register_hooks
function is called by the sudo front end to
register any hooks the plugin needs.
If the plugin does not support hooks,
.Li register_hooks
should be set to the
.Dv NULL
pointer.
.Pp
The
.Em version
argument describes the version of the hooks API
supported by the
.Nm sudo
front end.
.Pp
The
.Fn register_hook
function should be used to register any supported
hooks the plugin needs.
It returns 0 on success, 1 if the hook type is not supported and \-1
if the major version in
.Li struct hook
does not match the front end's major hook API version.
.Pp
See the
.Sx Hook function API
section below for more information
about hooks.
.Pp
NOTE: the
.Fn register_hooks
function is only available starting
with API version 1.2.
If the
.Nm sudo
front end doesn't support API
version 1.2 or higher,
.Li register_hooks
will not be called.
.It deregister_hooks
.Bd -literal -compact
void (*deregister_hooks)(int version,
   int (*deregister_hook)(struct sudo_hook *hook));
.Ed
.Pp
The
.Fn deregister_hooks
function is called by the sudo front end
to deregister any hooks the plugin has registered.
If the plugin does not support hooks,
.Li deregister_hooks
should be set to the
.Dv NULL
pointer.
.Pp
The
.Em version
argument describes the version of the hooks API
supported by the
.Nm sudo
front end.
.Pp
The
.Fn deregister_hook
function should be used to deregister any
hooks that were put in place by the
.Fn register_hook
function.
If the plugin tries to deregister a hook that the front end does not support,
.Li deregister_hook
will return an error.
.Pp
See the
.Sx Hook function API
section below for more information
about hooks.
.Pp
NOTE: the
.Fn deregister_hooks
function is only available starting
with API version 1.2.
If the
.Nm sudo
front end doesn't support API
version 1.2 or higher,
.Li deregister_hooks
will not be called.
.El
.Pp
.Em Policy Plugin Version Macros
.Bd -literal
/* Plugin API version major/minor. */
#define SUDO_API_VERSION_MAJOR 1
#define SUDO_API_VERSION_MINOR 2
#define SUDO_API_MKVERSION(x, y) ((x << 16) | y)
#define SUDO_API_VERSION SUDO_API_MKVERSION(SUDO_API_VERSION_MAJOR,\e
                                            SUDO_API_VERSION_MINOR)

/* Getters and setters for API version */
#define SUDO_API_VERSION_GET_MAJOR(v) ((v) >> 16)
#define SUDO_API_VERSION_GET_MINOR(v) ((v) & 0xffff)
#define SUDO_API_VERSION_SET_MAJOR(vp, n) do { \e
    *(vp) = (*(vp) & 0x0000ffff) | ((n) << 16); \e
} while(0)
#define SUDO_API_VERSION_SET_MINOR(vp, n) do { \e
    *(vp) = (*(vp) & 0xffff0000) | (n); \e
} while(0)
.Ed
.Ss I/O plugin API
.Bd -literal
struct io_plugin {
#define SUDO_IO_PLUGIN 2
    unsigned int type; /* always SUDO_IO_PLUGIN */
    unsigned int version; /* always SUDO_API_VERSION */
    int (*open)(unsigned int version, sudo_conv_t conversation,
                sudo_printf_t plugin_printf, char * const settings[],
                char * const user_info[], char * const command_info[],
                int argc, char * const argv[], char * const user_env[],
                char * const plugin_options[]);
    void (*close)(int exit_status, int error); /* wait status or error */
    int (*show_version)(int verbose);
    int (*log_ttyin)(const char *buf, unsigned int len);
    int (*log_ttyout)(const char *buf, unsigned int len);
    int (*log_stdin)(const char *buf, unsigned int len);
    int (*log_stdout)(const char *buf, unsigned int len);
    int (*log_stderr)(const char *buf, unsigned int len);
    void (*register_hooks)(int version,
       int (*register_hook)(struct sudo_hook *hook));
    void (*deregister_hooks)(int version,
       int (*deregister_hook)(struct sudo_hook *hook));
    int (*change_winsize)(unsigned int lines, unsigned int cols);
};
.Ed
.Pp
When an I/O plugin is loaded,
.Nm sudo
runs the command in a pseudo-tty.
This makes it possible to log the input and output from the user's
session.
If any of the standard input, standard output or standard error do not
correspond to a tty,
.Nm sudo
will open a pipe to capture
the I/O for logging before passing it on.
.Pp
The log_ttyin function receives the raw user input from the terminal
device (note that this will include input even when echo is disabled,
such as when a password is read).
The log_ttyout function receives output from the pseudo-tty that is
suitable for replaying the user's session at a later time.
The
.Fn log_stdin ,
.Fn log_stdout
and
.Fn log_stderr
functions are only called if the standard input, standard output
or standard error respectively correspond to something other than
a tty.
.Pp
Any of the logging functions may be set to the
.Dv NULL
pointer if no logging is to be performed.
If the open function returns 0, no I/O will be sent to the plugin.
.Pp
If a logging function returns an error
.Pq \-1 ,
the running command will be terminated and all of the plugin's logging
functions will be disabled.
Other I/O logging plugins will still receive any remaining
input or output that has not yet been processed.
.Pp
If an input logging function rejects the data by returning 0, the
command will be terminated and the data will not be passed to the
command, though it will still be sent to any other I/O logging plugins.
If an output logging function rejects the data by returning 0, the
command will be terminated and the data will not be written to the
terminal, though it will still be sent to any other I/O logging plugins.
.Pp
The io_plugin struct has the following fields:
.Bl -tag -width 4n
.It type
The
.Li type
field should always be set to
.Dv SUDO_IO_PLUGIN .
.It version
The
.Li version
field should be set to
.Dv SUDO_API_VERSION .
.Pp
This allows
.Nm sudo
to determine the API version the plugin was
built against.
.It open
.Bd -literal -compact
int (*open)(unsigned int version, sudo_conv_t conversation,
            sudo_printf_t plugin_printf, char * const settings[],
            char * const user_info[], int argc, char * const argv[],
            char * const user_env[], char * const plugin_options[]);
.Ed
.Pp
The
.Fn open
function is run before the
.Fn log_ttyin ,
.Fn log_ttyout ,
.Fn log_stdin ,
.Fn log_stdout ,
.Fn log_stderr ,
or
.Fn show_version
functions are called.
It is only called if the version is being requested or if the
policy plugin's
.Fn check_policy
function has returned successfully.
It returns 1 on success, 0 on failure, \-1 if a general error occurred,
or \-2 if there was a usage error.
In the latter case,
.Nm sudo
will print a usage message before it exits.
If an error occurs, the plugin may optionally call the
.Fn conversation
or
.Fn plugin_printf
function with
.Dv SUDO_CONF_ERROR_MSG
to present
additional error information to the user.
.Pp
The function arguments are as follows:
.Bl -tag -width 4n
.It version
The version passed in by
.Nm sudo
allows the plugin to determine the
major and minor version number of the plugin API supported by
.Nm sudo .
.It conversation
A pointer to the
.Fn conversation
function that may be used by the
.Fn show_version
function to display version information (see
.Fn show_version
below).
The
.Fn conversation
function may also be used to display additional error message to the user.
The
.Fn conversation
function returns 0 on success and \-1 on failure.
.It plugin_printf
A pointer to a
.Fn printf Ns -style
function that may be used by the
.Fn show_version
function to display version information (see
show_version below).
The
.Fn plugin_printf
function may also be used to display additional error message to the user.
The
.Fn plugin_printf
function returns number of characters printed on success and \-1 on failure.
.It settings
A vector of user-supplied
.Nm sudo
settings in the form of
.Dq name=value
strings.
The vector is terminated by a
.Dv NULL
pointer.
These settings correspond to flags the user specified when running
.Nm sudo .
As such, they will only be present when the corresponding flag has
been specified on the command line.
.Pp
When parsing
.Em settings ,
the plugin should split on the
.Sy first
equal sign
.Pq Ql =
since the
.Em name
field will never include one
itself but the
.Em value
might.
.Pp
See the
.Sx Policy plugin API
section for a list of all possible settings.
.It user_info
A vector of information about the user running the command in the form of
.Dq name=value
strings.
The vector is terminated by a
.Dv NULL
pointer.
.Pp
When parsing
.Em user_info ,
the plugin should split on the
.Sy first
equal sign
.Pq Ql =
since the
.Em name
field will never include one
itself but the
.Em value
might.
.Pp
See the
.Sx Policy plugin API
section for a list of all possible strings.
.It argc
The number of elements in
.Em argv ,
not counting the final
.Dv NULL
pointer.
.It argv
If
.No non- Ns Dv NULL ,
an argument vector describing a command the user
wishes to run in the same form as what would be passed to the
.Xr execve 2
system call.
.It user_env
The user's environment in the form of a
.Dv NULL Ns -terminated
vector of
.Dq name=value
strings.
.Pp
When parsing
.Em user_env ,
the plugin should split on the
.Sy first
equal sign
.Pq Ql =
since the
.Em name
field will never include one
itself but the
.Em value
might.
.It plugin_options
Any (non-comment) strings immediately after the plugin path are
treated as arguments to the plugin.
These arguments are split on a white space boundary and are passed to
the plugin in the form of a
.Dv NULL Ns -terminated
array of strings.
If no arguments were specified,
.Em plugin_options
will be the
.Dv NULL
pointer.
.Pp
NOTE: the
.Em plugin_options
parameter is only available starting with
API version 1.2.
A plugin
.Sy must
check the API version specified
by the
.Nm sudo
front end before using
.Em plugin_options .
Failure to do so may result in a crash.
.El
.It close
.Bd -literal -compact
void (*close)(int exit_status, int error);
.Ed
.Pp
The
.Fn close
function is called when the command being run by
.Nm sudo
finishes.
.Pp
The function arguments are as follows:
.Bl -tag -width 4n
.It exit_status
The command's exit status, as returned by the
.Xr wait 2
system call.
The value of
.Li exit_status
is undefined if
.Li error
is non-zero.
.It error
If the command could not be executed, this is set to the value of
.Li errno
set by the
.Xr execve 2
system call.
If the command was successfully executed, the value of
.Li error
is 0.
.El
.It show_version
.Bd -literal -compact
int (*show_version)(int verbose);
.Ed
.Pp
The
.Fn show_version
function is called by
.Nm sudo
when the user specifies
the
.Fl V
option.
The plugin may display its version information to the user via the
.Fn conversation
or
.Fn plugin_printf
function using
.Dv SUDO_CONV_INFO_MSG .
If the user requests detailed version information, the verbose flag will be set.
.It log_ttyin
.Bd -literal -compact
int (*log_ttyin)(const char *buf, unsigned int len);
.Ed
.Pp
The
.Fn log_ttyin
function is called whenever data can be read from
the user but before it is passed to the running command.
This allows the plugin to reject data if it chooses to (for instance
if the input contains banned content).
Returns 1 if the data should be passed to the command, 0 if the data
is rejected (which will terminate the running command) or \-1 if an
error occurred.
.Pp
The function arguments are as follows:
.Bl -tag -width 4n
.It buf
The buffer containing user input.
.It len
The length of
.Em buf
in bytes.
.El
.It log_ttyout
.Bd -literal -compact
int (*log_ttyout)(const char *buf, unsigned int len);
.Ed
.Pp
The
.Fn log_ttyout
function is called whenever data can be read from
the command but before it is written to the user's terminal.
This allows the plugin to reject data if it chooses to (for instance
if the output contains banned content).
Returns 1 if the data should be passed to the user, 0 if the data is rejected
(which will terminate the running command) or \-1 if an error occurred.
.Pp
The function arguments are as follows:
.Bl -tag -width 4n
.It buf
The buffer containing command output.
.It len
The length of
.Em buf
in bytes.
.El
.It log_stdin
.Bd -literal -compact
int (*log_stdin)(const char *buf, unsigned int len);
.Ed
.Pp
The
.Fn log_stdin
function is only used if the standard input does
not correspond to a tty device.
It is called whenever data can be read from the standard input but
before it is passed to the running command.
This allows the plugin to reject data if it chooses to
(for instance if the input contains banned content).
Returns 1 if the data should be passed to the command, 0 if the data is
rejected (which will terminate the running command) or \-1 if an error occurred.
.Pp
The function arguments are as follows:
.Bl -tag -width 4n
.It buf
The buffer containing user input.
.It len
The length of
.Em buf
in bytes.
.El
.It log_stdout
.Bd -literal -compact
int (*log_stdout)(const char *buf, unsigned int len);
.Ed
.Pp
The
.Fn log_stdout
function is only used if the standard output does not correspond
to a tty device.
It is called whenever data can be read from the command but before
it is written to the standard output.
This allows the plugin to reject data if it chooses to
(for instance if the output contains banned content).
Returns 1 if the data should be passed to the user, 0 if the data is
rejected (which will terminate the running command) or \-1 if an error occurred.
.Pp
The function arguments are as follows:
.Bl -tag -width 4n
.It buf
The buffer containing command output.
.It len
The length of
.Em buf
in bytes.
.El
.It log_stderr
.Bd -literal -compact
int (*log_stderr)(const char *buf, unsigned int len);
.Ed
.Pp
The
.Fn log_stderr
function is only used if the standard error does
not correspond to a tty device.
It is called whenever data can be read from the command but before it
is written to the standard error.
This allows the plugin to reject data if it chooses to
(for instance if the output contains banned content).
Returns 1 if the data should be passed to the user, 0 if the data is
rejected (which will terminate the running command) or \-1 if an error occurred.
.Pp
The function arguments are as follows:
.Bl -tag -width 4n
.It buf
The buffer containing command output.
.It len
The length of
.Em buf
in bytes.
.El
.It register_hooks
See the
.Sx Policy plugin API
section for a description of
.Li register_hooks .
.It deregister_hooks
See the
.Sx Policy plugin API
section for a description of
.Li deregister_hooks .
.It change_winsize
.Bd -literal -compact
int (*change_winsize)(unsigned int lines, unsigned int cols);
.Ed
.Pp
The
.Fn change_winsize
function is called whenever the window size of the terminal changes from
the initial values specified in the
.Li user_info
list.
It returns 1 on success, 0 on failure, \-1 if an error occurred (which
will terminate the running command).
.El
.Pp
.Em I/O Plugin Version Macros
.Pp
Same as for the
.Sx Policy plugin API .
.Ss Signal handlers
The
.Nm sudo
front end installs default signal handlers to trap common signals
while the plugin functions are run.
The following signals are trapped by default before the command is
executed:
.Pp
.Bl -bullet -compact -width 1n
.It
.Dv SIGALRM
.It
.Dv SIGHUP
.It
.Dv SIGINT
.It
.Dv SIGPIPE
.It
.Dv SIGQUIT
.It
.Dv SIGTERM
.It
.Dv SIGTSTP
.It
.Dv SIGUSR1
.It
.Dv SIGUSR2
.El
.Pp
If a fatal signal is received before the command is executed,
.Nm sudo
will call the plugin's
.Fn close
function with an exit status of 128 plus the value of the signal
that was received.
This allows for consistent logging of commands killed by a signal
for plugins that log such information in their
.Fn close
function.
An exception to this is
.Ev SIGPIPE ,
which is ignored until the command is executed.
.Pp
A plugin may temporarily install its own signal handlers but must
restore the original handler before the plugin function returns.
.Ss Hook function API
Beginning with plugin API version 1.2, it is possible to install
hooks for certain functions called by the
.Nm sudo
front end.
.Pp
Currently, the only supported hooks relate to the handling of
environment variables.
Hooks can be used to intercept attempts to get, set, or remove
environment variables so that these changes can be reflected in
the version of the environment that is used to execute a command.
A future version of the API will support hooking internal
.Nm sudo
front end functions as well.
.Pp
.Em Hook structure
.Pp
Hooks in
.Nm sudo
are described by the following structure:
.Bd -literal
typedef int (*sudo_hook_fn_t)();

struct sudo_hook {
    unsigned int hook_version;
    unsigned int hook_type;
    sudo_hook_fn_t hook_fn;
    void *closure;
};
.Ed
.Pp
The
.Li sudo_hook
structure has the following fields:
.Bl -tag -width 4n
.It hook_version
The
.Li hook_version
field should be set to
.Dv SUDO_HOOK_VERSION .
.It hook_type
The
.Li hook_type
field may be one of the following supported hook types:
.Bl -tag -width 4n
.It Dv SUDO_HOOK_SETENV
The C library
.Xr setenv 3
function.
Any registered hooks will run before the C library implementation.
The
.Li hook_fn
field should
be a function that matches the following typedef:
.Bd -literal
typedef int (*sudo_hook_fn_setenv_t)(const char *name,
   const char *value, int overwrite, void *closure);
.Ed
.Pp
If the registered hook does not match the typedef the results are
unspecified.
.It Dv SUDO_HOOK_UNSETENV
The C library
.Xr unsetenv 3
function.
Any registered hooks will run before the C library implementation.
The
.Li hook_fn
field should
be a function that matches the following typedef:
.Bd -literal
typedef int (*sudo_hook_fn_unsetenv_t)(const char *name,
   void *closure);
.Ed
.It Dv SUDO_HOOK_GETENV
The C library
.Xr getenv 3
function.
Any registered hooks will run before the C library implementation.
The
.Li hook_fn
field should
be a function that matches the following typedef:
.Bd -literal
typedef int (*sudo_hook_fn_getenv_t)(const char *name,
   char **value, void *closure);
.Ed
.Pp
If the registered hook does not match the typedef the results are
unspecified.
.It Dv SUDO_HOOK_PUTENV
The C library
.Xr putenv 3
function.
Any registered hooks will run before the C library implementation.
The
.Li hook_fn
field should
be a function that matches the following typedef:
.Bd -literal
typedef int (*sudo_hook_fn_putenv_t)(char *string,
   void *closure);
.Ed
.Pp
If the registered hook does not match the typedef the results are
unspecified.
.El
.It hook_fn
sudo_hook_fn_t hook_fn;
.Pp
The
.Li hook_fn
field should be set to the plugin's hook implementation.
The actual function arguments will vary depending on the
.Li hook_type
(see
.Li hook_type
above).
In all cases, the
.Li closure
field of
.Li struct sudo_hook
is passed as the last function parameter.
This can be used to pass arbitrary data to the plugin's hook implementation.
.Pp
The function return value may be one of the following:
.Bl -tag -width 4n
.It Dv SUDO_HOOK_RET_ERROR
The hook function encountered an error.
.It Dv SUDO_HOOK_RET_NEXT
The hook completed without error, go on to the next hook (including
the native implementation if applicable).
For example, a
.Xr getenv 3
hook might return
.Dv SUDO_HOOK_RET_NEXT
if the specified variable was not found in the private copy of the environment.
.It Dv SUDO_HOOK_RET_STOP
The hook completed without error, stop processing hooks for this invocation.
This can be used to replace the native implementation.
For example, a
.Li setenv
hook that operates on a private copy of
the environment but leaves
.Li environ
unchanged.
.El
.El
.Pp
Note that it is very easy to create an infinite loop when hooking
C library functions.
For example, a
.Xr getenv 3
hook that calls the
.Xr snprintf 3
function may create a loop if the
.Xr snprintf 3
implementation calls
.Xr getenv 3
to check the locale.
To prevent this, you may wish to use a static variable in the hook
function to guard against nested calls.
For example:
.Bd -literal
static int in_progress = 0; /* avoid recursion */
if (in_progress)
    return SUDO_HOOK_RET_NEXT;
in_progress = 1;
\&...
in_progress = 0;
return SUDO_HOOK_RET_STOP;
.Ed
.Pp
.Em Hook API Version Macros
.Bd -literal
/* Hook API version major/minor */
#define SUDO_HOOK_VERSION_MAJOR 1
#define SUDO_HOOK_VERSION_MINOR 0
#define SUDO_HOOK_VERSION SUDO_API_MKVERSION(SUDO_HOOK_VERSION_MAJOR,\e
                                              SUDO_HOOK_VERSION_MINOR)
.Ed
.Pp
For getters and setters see the
.Sx Policy plugin API .
.Ss Remote command execution
The
.Nm sudo
front end does not have native support for running remote commands.
However, starting with
.Nm sudo
1.8.8, the
.Fl h
option may be used to specify a remote host that is passed
to the policy plugin.
A plugin may also accept a
.Em runas_user
in the form of
.Dq user@hostname
which will work with older versions of
.Nm sudo .
It is anticipated that remote commands will be supported by executing a
.Dq helper
program.
The policy plugin should setup the execution environment such that the
.Nm sudo
front end will run the helper which, in turn, will connect to the
remote host and run the command.
.Pp
For example, the policy plugin could utilize
.Nm ssh
to perform remote command execution.
The helper program would be responsible for running
.Nm ssh
with the proper options to use a private key or certificate
that the remote host will accept and run a program
on the remote host that would setup the execution environment
accordingly.
.Pp
Note that remote
.Nm sudoedit
functionality must be handled by the policy plugin, not
.Nm sudo
itself as the front end has no knowledge that a remote command is
being executed.
This may be addressed in a future revision of the plugin API.
.Ss Conversation API
If the plugin needs to interact with the user, it may do so via the
.Fn conversation
function.
A plugin should not attempt to read directly from the standard input
or the user's tty (neither of which are guaranteed to exist).
The caller must include a trailing newline in
.Li msg
if one is to be printed.
.Pp
A
.Fn printf Ns -style
function is also available that can be used to display informational
or error messages to the user, which is usually more convenient for
simple messages where no use input is required.
.Pp
.Em Conversation function structures
.Pp
The conversation function takes as arguments pointers to the following
structures:
.Bd -literal
struct sudo_conv_message {
#define SUDO_CONV_PROMPT_ECHO_OFF  0x0001 /* do not echo user input */
#define SUDO_CONV_PROMPT_ECHO_ON   0x0002 /* echo user input */
#define SUDO_CONV_ERROR_MSG        0x0003 /* error message */
#define SUDO_CONV_INFO_MSG         0x0004 /* informational message */
#define SUDO_CONV_PROMPT_MASK      0x0005 /* mask user input */
#define SUDO_CONV_PROMPT_ECHO_OK   0x1000 /* flag: allow echo if no tty */
#define SUDO_CONV_PREFER_TTY       0x2000 /* flag: use tty if possible */
    int msg_type;
    int timeout;
    const char *msg;
};

#define SUDO_CONV_REPL_MAX      255

struct sudo_conv_reply {
    char *reply;
};

typedef int (*sudo_conv_callback_fn_t)(int signo, void *closure);
struct sudo_conv_callback {
    unsigned int version;
    void *closure;
    sudo_conv_callback_fn_t on_suspend;
    sudo_conv_callback_fn_t on_resume;
};
.Ed
.Pp
Pointers to the
.Fn conversation
and
.Fn printf Ns -style
functions are passed
in to the plugin's
.Fn open
function when the plugin is initialized.
The following type definitions can be used in the declaration of the
.Fn open
function:
.Bd -literal
typedef int (*sudo_conv_t)(int num_msgs,
             const struct sudo_conv_message msgs[],
             struct sudo_conv_reply replies[],
	     struct sudo_conv_callback *callback);

typedef int (*sudo_printf_t)(int msg_type, const char *fmt, ...);
.Ed
.Pp
To use the
.Fn conversation
function, the plugin must pass an array of
.Li sudo_conv_message
and
.Li sudo_conv_reply
structures.
There must be a
.Li struct sudo_conv_message
and
.Li struct sudo_conv_reply
for
each message in the conversation.
The
.Li struct sudo_conv_callback
pointer, if not
.Dv NULL ,
should contain function pointers to be called when the
.Nm sudo
process is suspended and/or resumed during conversation input.
The
.Fa on_suspend
and
.Fa on_resume
functions are called with the signal that caused
.Nm sudo
to be suspended and the
.Fa closure
pointer from the
.Li struct sudo_conv_callback .
These functions should return 0 on success and \-1 on error.
On error, the conversation will end and the conversation function
will return a value of \-1.
The intended use is to allow the plugin to release resources, such as locks,
that should not be held indefinitely while suspended and then reacquire them
when the process is resumed.
Note that the functions are not actually invoked from within a signal handler.
.Pp
The
.Em msg_type
must be set to one of the following values:
.Bl -tag -width 4n
.It SUDO_CONV_PROMPT_ECHO_OFF
Prompt the user for input with echo disabled;
this is generally used for passwords.
The reply will be stored in the
.Em replies
array.
.It SUDO_CONV_PROMPT_ECHO_ON
Prompt the user for input with echo enabled.
The reply will be stored in the
.Em replies
array.
.It SUDO_CONV_ERROR_MSG
Display an error message.
The message is written to the standard error unless the
.Dv SUDO_CONV_PREFER_TTY
flag is set, in which case it is written to the user's terminal if possible.
.It SUDO_CONV_INFO_MSG
Display a message.
The message is written to the standard output unless the
.Dv SUDO_CONV_PREFER_TTY
flag is set, in which case it is written to the user's terminal if possible.
.It SUDO_CONV_PROMPT_MASK
Prompt the user for input but echo an asterisk character for each
character read.
The reply will be stored in the
.Em replies
This can be used to provide visual feedback to the user while reading
sensitive information that should not be displayed.
.El
.Pp
In addition to the above values, the following flag bits may also be set:
.Bl -tag -width 4n
.It SUDO_CONV_PROMPT_ECHO_OK
Allow input to be read when echo cannot be disabled
when the message type is
.Dv SUDO_CONV_PROMPT_ECHO_OFF
or
.Dv SUDO_CONV_PROMPT_MASK .
By default,
.Nm sudo
will refuse to read input if the echo cannot be disabled for those
message types.
.It SUDO_CONV_PREFER_TTY
When displaying a message via
.Dv SUDO_CONV_ERROR_MSG
or
.Dv SUDO_CONV_INFO_MSG ,
try to write the message to the user's terminal.
If the terminal is unavailable, the standard error or standard output
will be used, depending upon whether
The user's terminal is always used when possible for input,
this flag is only used for output.
.Dv SUDO_CONV_ERROR_MSG
or
.Dv SUDO_CONV_INFO_MSG
was used.
.El
.Pp
The plugin is responsible for freeing the reply buffer located in each
.Li struct sudo_conv_reply ,
if it is not
.Dv NULL .
.Dv SUDO_CONV_REPL_MAX
represents the maximum length of the reply buffer (not including
the trailing NUL character).
In practical terms, this is the longest password
.Nm sudo
will support.
It is also useful as a maximum value for the
.Fn memset_s
function when clearing passwords filled in by the conversation function.
.Pp
The
.Fn printf Ns -style
function uses the same underlying mechanism as the
.Fn conversation
function but only supports
.Dv SUDO_CONV_INFO_MSG
and
.Dv SUDO_CONV_ERROR_MSG
for the
.Em msg_type
parameter.
It can be more convenient than using the
.Fn conversation
function if no user reply is needed and supports standard
.Fn printf
escape sequences.
.Pp
See the sample plugin for an example of the
.Fn conversation
function usage.
.Ss Sudoers group plugin API
The
.Nm sudoers
plugin supports its own plugin interface to allow non-Unix
group lookups.
This can be used to query a group source other than the standard Unix
group database.
Two sample group plugins are bundled with
.Nm sudo ,
.Em group_file
and
.Em system_group ,
are detailed in
.Xr sudoers @mansectform@ .
Third party group plugins include a QAS AD plugin available from Quest Software.
.Pp
A group plugin must declare and populate a
.Li sudoers_group_plugin
struct in the global scope.
This structure contains pointers to the functions that implement plugin
initialization, cleanup and group lookup.
.Bd -literal
struct sudoers_group_plugin {
   unsigned int version;
   int (*init)(int version, sudo_printf_t sudo_printf,
               char *const argv[]);
   void (*cleanup)(void);
   int (*query)(const char *user, const char *group,
                const struct passwd *pwd);
};
.Ed
.Pp
The
.Li sudoers_group_plugin
struct has the following fields:
.Bl -tag -width 4n
.It version
The
.Li version
field should be set to GROUP_API_VERSION.
.Pp
This allows
.Nm sudoers
to determine the API version the group plugin
was built against.
.It init
.Bd -literal -compact
int (*init)(int version, sudo_printf_t plugin_printf,
            char *const argv[]);
.Ed
.Pp
The
.Fn init
function is called after
.Em sudoers
has been parsed but
before any policy checks.
It returns 1 on success, 0 on failure (or if the plugin is not configured),
and \-1 if a error occurred.
If an error occurs, the plugin may call the
.Fn plugin_printf
function with
.Dv SUDO_CONF_ERROR_MSG
to present additional error information
to the user.
.Pp
The function arguments are as follows:
.Bl -tag -width 4n
.It version
The version passed in by
.Nm sudoers
allows the plugin to determine the
major and minor version number of the group plugin API supported by
.Nm sudoers .
.It plugin_printf
A pointer to a
.Fn printf Ns -style
function that may be used to display informational or error message to the user.
Returns the number of characters printed on success and \-1 on failure.
.It argv
A
.Dv NULL Ns -terminated
array of arguments generated from the
.Em group_plugin
option in
.Em sudoers .
If no arguments were given,
.Em argv
will be
.Dv NULL .
.El
.It cleanup
.Bd -literal -compact
void (*cleanup)();
.Ed
.Pp
The
.Fn cleanup
function is called when
.Nm sudoers
has finished its
group checks.
The plugin should free any memory it has allocated and close open file handles.
.It query
.Bd -literal -compact
int (*query)(const char *user, const char *group,
             const struct passwd *pwd);
.Ed
.Pp
The
.Fn query
function is used to ask the group plugin whether
.Em user
is a member of
.Em group .
.Pp
The function arguments are as follows:
.Bl -tag -width 4n
.It user
The name of the user being looked up in the external group database.
.It group
The name of the group being queried.
.It pwd
The password database entry for
.Em user ,
if any.
If
.Em user
is not
present in the password database,
.Em pwd
will be
.Dv NULL .
.El
.El
.Pp
.Em Group API Version Macros
.Bd -literal
/* Sudoers group plugin version major/minor */
#define GROUP_API_VERSION_MAJOR 1
#define GROUP_API_VERSION_MINOR 0
#define GROUP_API_VERSION ((GROUP_API_VERSION_MAJOR << 16) | \e
                           GROUP_API_VERSION_MINOR)
.Ed
For getters and setters see the
.Sx Policy plugin API .
.Sh PLUGIN API CHANGELOG
The following revisions have been made to the Sudo Plugin API.
.Bl -tag -width 4n
.It Version 1.0
Initial API version.
.It Version 1.1 (sudo 1.8.0)
The I/O logging plugin's
.Fn open
function was modified to take the
.Li command_info
list as an argument.
.It Version 1.2 (sudo 1.8.5)
The Policy and I/O logging plugins'
.Fn open
functions are now passed
a list of plugin parameters if any are specified in
.Xr sudo.conf @mansectform@ .
.Pp
A simple hooks API has been introduced to allow plugins to hook in to the
system's environment handling functions.
.Pp
The
.Li init_session
Policy plugin function is now passed a pointer
to the user environment which can be updated as needed.
This can be used to merge in environment variables stored in the PAM
handle before a command is run.
.It Version 1.3 (sudo 1.8.7)
Support for the
.Em exec_background
entry has been added to the
.Li command_info
list.
.Pp
The
.Em max_groups
and
.Em plugin_dir
entries were added to the
.Li settings
list.
.Pp
The
.Fn version
and
.Fn close
functions are now optional.
Previously, a missing
.Fn version
or
.Fn close
function would result in a crash.
If no policy plugin
.Fn close
function is defined, a default
.Fn close
function will be provided by the
.Nm sudo
front end that displays a warning if the command could not be
executed.
.Pp
The
.Nm sudo
front end now installs default signal handlers to trap common signals
while the plugin functions are run.
.It Version 1.4 (sudo 1.8.8)
The
.Em remote_host
entry was added to the
.Li settings
list.
.It Version 1.5 (sudo 1.8.9)
The
.Em preserve_fds
entry was added to the
.Li command_info
list.
.It Version 1.6 (sudo 1.8.11)
The behavior when an I/O logging plugin returns an error
.Pq \-1
has changed.
Previously, the
.Nm sudo
front end took no action when the
.Fn log_ttyin ,
.Fn log_ttyout ,
.Fn log_stdin ,
.Fn log_stdout ,
or
.Fn log_stderr
function returned an error.
.Pp
The behavior when an I/O logging plugin returns 0 has changed.
Previously, output from the command would be displayed to the
terminal even if an output logging function returned 0.
.It Version 1.7 (sudo 1.8.12)
The
.Em plugin_path
entry was added to the
.Li settings
list.
.Pp
The
.Em debug_flags
entry now starts with a debug file path name and may occur multiple
times if there are multiple plugin-specific Debug lines in the
.Xr sudo.conf @mansectform@ file.
.It Version 1.8 (sudo 1.8.15)
The
.Em sudoedit_checkdir
and
.Em sudoedit_follow
entries were added to the
.Li command_info
list.
The default value of
.Em sudoedit_checkdir
was changed to true in sudo 1.8.16.
.Pp
The sudo
.Em conversation
function now takes a pointer to a
.Li struct sudo_conv_callback
as its fourth argument.
The
.Li sudo_conv_t
definition has been updated to match.
The plugin must specify that it supports plugin API version 1.8 or higher
to receive a conversation function pointer that supports this argument.
.It Version 1.9 (sudo 1.8.16)
The
.Em execfd
entry was added to the
.Li command_info
list.
.It Version 1.10 (sudo 1.8.19)
The
.Em umask
entry was added to the
.Li user_info
list.
The
.Em iolog_group ,
.Em iolog_mode ,
and
.Em iolog_user
entries were added to the
.Li command_info
list.
.It Version 1.11 (sudo 1.8.20)
The
.Em timeout
entry was added to the
.Li settings
list.
.It Version 1.12 (sudo 1.8.21)
The
.Li change_winsize
field was added to the io_plugin struct.
.El
.Sh SEE ALSO
.Xr sudo.conf @mansectform@ ,
.Xr sudoers @mansectform@ ,
.Xr sudo @mansectsu@
.Sh AUTHORS
Many people have worked on
.Nm sudo
over the years; this version consists of code written primarily by:
.Bd -ragged -offset indent
.An Todd C. Miller
.Ed
.Pp
See the CONTRIBUTORS file in the
.Nm sudo
distribution (https://www.sudo.ws/contributors.html) for an
exhaustive list of people who have contributed to
.Nm sudo .
.Sh BUGS
If you feel you have found a bug in
.Nm sudo ,
please submit a bug report at https://bugzilla.sudo.ws/
.Sh SUPPORT
Limited free support is available via the sudo-users mailing list,
see https://www.sudo.ws/mailman/listinfo/sudo-users to subscribe or
search the archives.
.Sh DISCLAIMER
.Nm sudo
is provided
.Dq AS IS
and any express or implied warranties, including, but not limited
to, the implied warranties of merchantability and fitness for a
particular purpose are disclaimed.
See the LICENSE file distributed with
.Nm sudo
or https://www.sudo.ws/license.html for complete details.
